A polyetherketone resin [such as a polyetheretherketone (PEEK) or a polyetherketone (PEK)] is a typical semicrystalline thermoplastic resin having excellent heat resistance, chemical resistance, mechanical strength, and others. The polyetherketone resin was developed by ICI in 1978, since then the resin has been used for various application fields, with which the conventional synthetic resins could not cope.
As one of characteristics of PEEK and PEK, which are different from the conventional thermoplastic resins, a higher-order structure thereof is exemplified. A common semicrystalline thermoplastic resin usually has a crystalline phase and an amorphous phase in a solidified state thereof. On the other hand, a polymer compound having a benzene ring or a naphthalene ring in a main chain thereof (e.g., a PEEK and a PEK) has a low-motile amorphous phase called a rigid amorphous, in addition to the crystalline phase and the amorphous phase, which was, for example, reported by a research team of Tokyo Institute of Technology in Society of Polymer Science, Japan, Annual Meeting, in 1999 [Nonpatent Document 1 (Polymer Preprints, Japan, vol. 48, No. 14, p. 3735, 1999)]. Due to such a complex higher-order structure, the polymer compound usually has a large dependency on the molecular weight and the molecular weight distribution of physical properties (particularly, the melt viscosity or the crystallization rate) compared with the common semicrystalline polymer. Furthermore, such a large dependency has great effects on mechanical properties of the product after molding process, which are influenced by the melt viscosity or the crystallization rate. On the other hand, the polymerization process for the PEEK or the PEK is very complicated compared with the conventional common synthetic resins in the following respects: the particularity of a solvent to be used, the high polymerization temperature or high viscosity derived from a high melting point (Tm) or glass transition temperature (Tg) of a synthesized polymer, the necessity of a step for washing a solvent or a remaining monomer in a final process of polymerization, and others. Thus, for example, it is not necessarily easy to develop various grades of polyetherketone resins with different molecular weights by controlling the polymerization reaction, differently from a polyamide resin or a polyester resin. Further, it is more difficult to control the molecular weight distribution, and a grade having a suitable moldability according to application has not been necessarily provided in the market.
Thus, the higher-order structure (e.g., crystal structure) of the polyetherketone resin is complicated. Compared with a common thermoplastic resin, it is difficult to precisely adjust the higher-order structure of the polyetherketone resin by the polymerization condition, due to a low solubility or a high melt viscosity thereof. Moreover, when the higher-order structure cannot be adjusted precisely, it is difficult to stably obtain a polyetherketone resin having a desired melt viscosity or crystallization temperature, and others. In order to stably obtain a molded product having desired mechanical properties from such a polyetherketone resin, enough consideration is needed for a molding process thereof. In particular, the melt viscosity or the crystallization temperature has effects on not only the strength of the molded product but also the working efficiency in a molding process thereof. Therefore, a large technical problem is how to adjust the melt viscosity or the crystallization temperature.
The method for obtaining a resin composition having desired physical properties includes, for example, a method which comprises adding two or more resins suitably. Japanese Patent Application Laid-Open No. 2006-241201 (Patent Document 1, JP-2006-241201A) discloses a styrene-series resin composition comprising (A) one of more styrene-series resins and (B) a thermoplastic resin other than a styrene-series resin, and having a bi-phase continuous structure having a structural period of 0.001 to 1 μm or a dispersed structure having a intergranular distance of 0.001 to 1 μm, wherein the melt viscosity ratio of these components at 180 to 300° C. and a shear rate of 1000 s−1 [the component (A)/the component (B)] is not less than 0.1. However, the styrene-series resin is not a crystalline thermoplastic resin and cannot improve the molding cycle even by mixing two kinds of resins.
Japanese Patent Application Laid-Open No. 2008-528768 (Patent Document 2, JP-2008-528768A) discloses a method of manufacturing an electrically conductive composition comprising forming a reduced viscosity molten masterbatch by mixing a molten masterbatch with a first polymer, wherein the first polymer has a melt viscosity that is lower than the melt viscosity of the molten masterbatch; and mixing the reduced viscosity masterbatch with a second polymer. However, the molten masterbatch is mixed with the first polymer having a different melt viscosity in order to improve the compatibility with the second polymer, and the mixture is mixed with the second polymer. Thus, such a mixing has a small effect on the molding cycle and the mechanical properties of a molded product thereof.
Japanese Patent Application Laid-Open No. 2007-506833 (Patent Document 3, JP-2007-506833A) discloses that a pack comprising a polymeric material having a melt viscosity (MV) in the range 0.05 to 0.12 kNsm−2 wherein said polymeric material is of a type which includes: (a) phenyl moieties, (b) carbonyl moieties, and (c) ether moieties. This document also discloses a mixture containing a plurality of low-viscosity polyetheretherketones. However, since the low-viscosity polyetheretherketones are mixed together to obtain a highly packing material, the molding cycle or the mechanical properties of a molded product thereof cannot be improved.
WO2009/057255 publication (Patent Document 4) discloses a polyetheretherketone comprising (A) a polymerization component having a molecular weight of not lower than 5,000 and lower than 2,000,000 and (B) a polymerization component having a molecular weight of not lower than 1,000 and lower than 5,000, wherein the weight ratio of (A):(B) is 60:40 to 97:3. However, since the polyetheretherketone contains the oligomer component (B) in addition to the resin component (A), the mechanical properties are deteriorated while improving the flowability.